Catalytic pyrolysis process (CPP) is a petrochemical process used for cracking a liquid hydrocarbon feed that utilizes both heat and catalytic action to crack the feed and generate light olefins and aromatics. Light olefins include unsaturated aliphatic hydrocarbons generally having, for example, two to eight carbon atoms and including one or more double bonds, with preference often given toward generation of ethylene, propylene, butylenes, butadiene, and aromatics such as benzene, toluene, and xylenes. CPP process and CPP reactors are somewhat analogous to fluidized catalytic cracking (FCC) processes and reactors, except CPP utilizes steam as a diluent, similar to steam cracking, and commonly CPP reactors operate at higher temperatures (e.g., +150° C.) than FCC reactors. Feeds for CPP and FCC processes (collectively, “catalytic cracking processes”) are preferably substantially free (e.g., <5 ppmw) of metals and other non-volatile components to avoid deactivation or contamination of the catalyst. High concentrations of metallic contaminants in a feed to a cat cracking process (e.g., >10 ppmw) leads to rapid catalyst fouling or contamination. The metallic contaminants tend to deposit and plug the pores or otherwise deactivate catalyst in a catalytic cracking reactor. The metals may be in the form of metal compounds, and/or organo-metallic compounds such as metal-containing porphyrins or porphyrin-like complexes.
Many liquid hydrocarbon feeds, such as naphthas, are substantially free of such contaminants or contain only an acceptably small portion and are thus suitable as cat cracking feed. Other feeds require more preliminary processing and preparation for generation of a suitable cat cracking feed stream. In some feed preparation processes, the liquid feed may be preliminarily processed, such as via desalting by water wash, but otherwise has substantially no non-volatile content. More contaminated feeds however, may be subjected to more substantial and costly processing to remove selected suitable fractions therefrom, such as via distillation, whereby the feed is fractionated into various cuts, such as gasoline, kerosene, naphtha, gas-oil (vacuum or atmospheric) and the like, which may be fed to a cat cracking process. Undesirable non-volatile components may be removed therefrom, including a higher boiling point bottoms component commonly referred to as residuum (“resid”), having for example, final boiling point of greater than 650° F. (343° C.), at atmospheric pressure. Commonly, the resid fractions remaining in the bottoms of the towers are not used for catalytic cracking feed and are typically disposed to low value uses. Multi-step separation processes such as distillation or fractionation typically require use of costly towers, refinery equipment, valuable storage space, and related processes, and typically only a limited portion of the original feed, if any, may be used as cat cracking feed. The higher costs associated with such expensive preliminary processes typically precludes so treating economically advantageous, lower cost feeds. Often use of feeds from treated refinery feed sources (e.g., such as feed for fluidized catalytic cracking processes, FCC, as used in gasoline manufacture) are more costly and useful for higher value processes than as cat cracking feed.
Patents are known to have addressed some aspects of the above-mentioned challenges posed with treating metal-laden liquid hydrocarbon feedstocks, but need for further improved processes remains. For example:
U.S. Pat. No. 4,257,871, incorporated herein by reference in its entirety, discloses using vacuum residue for production of olefins by first separating, preferably by solvent extraction, the asphalt therein, blending resultant asphalt-depleted fraction with a lighter fraction, e.g., a vacuum gas oil, and then subjecting the blend to a conventional catalytic hydrogenation step prior to thermal cracking. The hydrogenate may be separated into fractions with the heavy fraction only being thermally cracked.
U.S. Pat. No. 4,992,163, incorporated herein by reference in its entirety, discloses a method of reducing the concentration of metal contaminants, such as vanadium and nickel, in distillates of a fossil fuel feedstock, comprising producing a selected distillate fraction and demetallizing the distillate by, for example hydroprocessing, precipitation or deasphalting, thereby upgrading and making it suitable for use as feed to a catalytic cracker.
U.S. Pat. No. 5,009,768, incorporated herein by reference in its entirety, discloses a hydrocatalytic process for treating vacuum gas oils, residual feedstocks or mixtures thereof in the presence of up to 100 ppm of V and Ni at moderate hydrogen partial pressures. The process consists of two or more stages: (a) demetallization of feedstock to levels below 10 ppm of V and Ni, and (b) hydrodenitrogenation and hydroconversion of catalysts using a combined bed, and catalytic cracking of the 370° C.+/− fraction to obtain gasolines.
Despite the above advances, the art needs a simplified, more economical process that can treat a wider range of hydrocarbon feedstocks, particularly cost advantaged, metal contaminated feeds, and convert a high weight percentage of such feed to a vaporizable feedstock useful as feed for catalytic cracking processes. It is also desirable to have a simplified process and apparatus that utilizes a single vessel that can adequately feed a catalytic cracking complex, such as but not limited to a PCC or FCC complex having multiple crackers.